The human skeleton is composed of 206 individual bones that perform a variety of important functions, including support, movement, protection, storage of minerals, and formation of blood cells. To ensure that the skeleton retains its ability to perform these functions, and to reduce pain and disfigurement, bones that become fractured should be repaired promptly and properly. Typically, a fractured bone is treated using a fixation device, which reinforces the fractured bone and keeps it aligned during healing. Fixation devices may take a variety of forms, including casts and fixators for external fixation, and bone plates, rods, and bone screws for internal fixation, among others.
Intramedullary rods/nails may function as fixation devices that are received longitudinally in the medullary canal of a broken and/or cut bone. For installation of an intramedullary rod, the medullary canal may be accessed from an end and/or side of the bone with an instrument such as an awl or saw. The medullary canal also may be prepared to receive the intramedullary rod by forming a longitudinal hole in the canal and/or by enlarging the canal. After intramedullary rod placement into the medullary canal, the rod may be secured in position using fasteners, for example, by attaching the rod to two or more bone fragments disposed on opposing sides of a break or cut in the bone. The intramedullary rod thus may include a plurality of transverse apertures that receive threaded fasteners, such as bone screws, which may be anchored in bone adjacent each aperture via an external thread. However, intramedullary rods with transverse apertures generally do not provide a straightforward mechanism for adjusting longitudinal compression of the bone. Accordingly, bone fragments fixed with an intramedullary rod may not be juxtaposed sufficiently for proper healing.
FIG. 1 shows a fixation device 40 that provides a distinct approach to supporting a bone by device placement in the medullary canal, as disclosed by U.S. Pat. No. 3,763,855 to McAtee (“the '855 patent”), which is incorporated herein by reference. Device 40 is disclosed to be suitable for fixation of ulna fractures, particularly in the olecranon region (the elbow protuberance) of the ulna. The device includes a fixation pin 42 for placement longitudinally into the medullary canal of the ulna from the proximal end thereof (i.e., through the elbow protuberance of the ulna). The device also includes a cortical fixation unit 44 for placement transversely into the ulna and medullary canal at a position intermediate the opposing ends of the ulna. Fixation pin 42 provides a slender, flexible body 46 with an external thread 48 extending along a majority of the length of the body. Cortical fixation unit 44 defines an internally threaded aperture 50 that threadably receives external thread 48 to lock fixation pin 42 to fixation unit 44. Fixation pin 42 also includes a head 52 to restrict advancement of the fixation pin into bone. In particular, fixation device 40 is disclosed to include a washer 54 slidably received on body 46 such that, as the fixation pin is advanced to its fully installed configuration, the washer engages a proximal end of the ulna and provides a bearing surface for head 52. The fixation pin also has a tip 56 to facilitate placement of the fixation pin into aperture 50 of cortical fixation unit 44.
FIG. 2 shows a holder 60 from the '855 patent for holding cortical fixation unit 44 during installation of fixation device 40. Holder 60 has a body 62 that defines a channel 64 for receiving a head 66 of the cortical fixation unit. In particular, body 62 includes a pair of opposing fingers 68 that extend to an underside 70 of head 66 to restrict longitudinal movement of the cortical fixation unit. Lateral movement of the cortical fixation unit is restricted by a retainer shaft 72 that is urged against outer surface 74 of head 66, such that a pointed end of the retainer shaft enters a recess 76 of head 66 of the cortical fixation unit.
The fixation device disclosed by the '855 patent may have some advantages over standard intramedullary rods/nails that define apertures for receiving fasteners. For example, the external thread extending along most of the length of fixation pin 42 allows a practitioner to place cortical fixation unit 44 crosswise into the ulna over a broad range of permitted positions along the ulna, to accommodate fractures disposed at different positions along the ulna. In addition, because fixation pin 42 is slender, the fixation pin can be driven along the medullary canal without the need for a previously formed hole in the medullary canal to receive the fixation pin. Furthermore, since fixation pin 42 is flexible and because the slender fixation pin can create its own path along the medullary canal, the fixation pin may be advanced along a nonlinear path in the medullary canal, thereby following the medullary canal as the canal bends as it extends along the bone.
However, the potential advantages of the fixation device disclosed by the '855 patent are offset by substantial disadvantages, making the fixation device difficult to install and/or inadequate for stable fixation. For example, placement of fixation pin 42 into aperture 50 of cortical fixation unit 44 inside bone, where tip 56 and aperture 50 are not visible, may be challenging, frustrating, and time-consuming. The difficulty of placement may be exacerbated further by a natural bend in the medullary canal, as the medullary canal extends away from the olecranon region. The bend in the medullary canal tends to flex the linear fixation pin as the pin is advanced along the canal, thus biasing the pin toward a side of the canal and preventing tip 56 from being re-positioned laterally by a practitioner while trying to feed tip 56 into aperture 50 of the fixation unit. Placement of fixation pin 42 into aperture 50 also may be hampered if the cortical fixation unit 44 is not oriented accurately in bone. In this regard, holder 60 of the '855 patent may not provide optimal positioning and manipulation of cortical fixation unit 44. Furthermore, the flexibility of fixation pin 42 may permit unwanted flexion after installation such that the bone is not fixed stably.